In exterior building construction utilizing aluminum or plastic siding panels, it is conventionally necessary to conceal the ends of strips of siding which occur at corners or at windows and doors by the use of J-tracks. These tracks have a J-shaped cross-section, with the long leg of the J facing against the supporting structure of the building to serve as a nailing flange and with the short leg of the J being exposed in front of the siding panel. Thus, the raw ends or edges of the siding panel are received in the pocket formed behind the short leg of the J. When the siding comes up to the lateral edges of a door or window, the bottom of the loop of the J abuts the side of the door or window frame.
While the use of J-tracks is common and acceptable for typical vertical or horizontal edges conventionally associated with the perimeter of windows and doors, such tracks cannot easily or practically be used to finish the edges around circular or curved inserts in an exterior wall, such as may be associated with decorative windows or louvres. The problem which arises in connection with such curved edges is the difficulty of obtaining a clean edge because the legs or flanges of the J-track must be slit or notched every inch or so to permit such track to conform to the curving perimeter of the rounded or circular window or vent which is being applied to the wall.
The use of a J-track in such applications could be avoided if there were a feasible way to form a recess or undercut around the perimeter of the curved window or louvre insert. Such an undercut, if it is to be formed in a molded plastic insert, must generally be created by the use of a mold insert which remains a part of the finished product or, in injection molding, by the use of slides in the mold. The use of slides, however, is generally not feasible in vacuum-forming because such slides interfere with the ability to clamp the plastic blank in place over the cavity of a vacuum-forming mold.
Accordingly, it is the primary object of the present invention to provide a vacuum-formed window or vent insert, and the method of making such insert, wherein the perimeter can be curved and formed with an undercut to receive the adjacent edges of the aluminum or plastic siding.